Mesopolitics describes the politics of intermediary structures within a political system, such as national political parties or movements.[65]

A political party is a political organization that typically seeks to attain and maintain political power within government, usually by participating in political campaigns, educational outreach, or protest actions. Parties often espouse an expressed ideology or vision, bolstered by a written platform with specific goals, forming a coalition among disparate interests.[66]

Political parties within a particular political system together form the party system, which can be either multiparty, two-party, dominant-party, or one-party, depending on the level of pluralism. This is affected by characteristics of the political system, including its electoral system. According to Duverger's law, first-past-the-post systems are likely to lead to two-party systems, while proportional representation systems are more likely to create a multiparty system.